1. Field of the Invention
The present invention relates to a developing device employing so-called trickle development technology, and an image forming apparatus including the same.
2. Description of Related Art
Some electrophotographic image forming apparatuses include a trickle developing device which supplies a photoreceptor drum with a two-component developer, which contains carrier and toner, thereby developing an electrostatic latent image formed on a circumferential surface of the photoreceptor drum. In the trickle developing device, a developer container constantly discharges a small and fixed amount of developer, and is replenished with a developer, which includes toner mixed with a small amount of carrier, in accordance with the amount of toner remaining in the developer container.
An example of the trickle developing device is described in Japanese Patent Laid-Open Publication No. 2000-66500. In this developing device, the interior space of the developer container is divided by a partition into first and second developer compartments in which the developer is circulated. The first developer compartment and the second developer compartment respectively include a first conveyance member and a second conveyance member, which are disposed horizontally and have rotating blades in order to convey the developer. Moreover, the first conveyance member is positioned along a developing roller so as to face the developing roller. The second developer compartment has a developer discharge port provided in its top portion. In the second developer compartment, the force of the second conveyance member conveying the developer by the rotating blade is low in some sections positioned on the downstream side with respect to the discharge port. Accordingly, the developer accumulates in such sections, and the upper level of the developer becomes higher than in the other sections.
In Japanese Patent Laid-Open Publication No. 2000-66500, to reduce the conveyance force in the aforementioned sections, the rotating blade of the second conveyance member gradually decrease in diameter toward the downstream side. Accordingly, for example, in the case where the image forming apparatus is installed in an unlevel place, so that the developing device is slanted, some developer accumulating in such sections might flow out of the space between the second conveyance member and the developer container. In such a case, the amount of developer conveyed in the first developer compartment and the second developer compartment varies over time, so that the amount of developer ejected from the discharge port becomes more likely to vary, resulting in reduced image quality.
Furthermore, recent image forming apparatuses might be required to print out more pages per unit time (i.e., increase print speed), or perform printing at various speeds. However, if the speed of developer conveyance is increased or rendered variable in order to meet such requirements, the amount of developer ejected from the discharge port still becomes more likely to vary.